In a vehicle, drivebility may be a concern when the overall vehicle torque crosses the lash zone through the driveline, which may include the transmission gear system, driveline joints, and wheels. The lash zone is when the total vehicle torque changes direction, i.e. from positive torque to negative torque, or vice versa. Lash, or backlash may occur for example due to lost motion caused by slack or clearance within various driveline components when the vehicle torque changes direction, such as during a driver tip in or tip out event. The vehicle torque is made up of the road load torque and torque provided by the prime mover(s) of the vehicle.
In a conventional vehicle, an opened torque converter may be utilized to help damp out the lash zone oscillation with an associated fuel economy penalty. In some of the recent dual clutch transmission without a torque converter, the engine torque going in and out of the lash zone needs to be controlled in order to reduce the lash zone oscillation and improve the torque response afterwards. Other methods to reduce lash may also be used including spark retardation within the engine, which may lead to reduced fuel efficiency and increased torque loading or oscillations on the engine. In a hybrid vehicle, controlling lash in the driveline becomes more complex as there may be more than one prime mover providing torque to the driveline.